In manufacturing processes it is frequently necessary to join together two or more substrates, for example two metal panels, or a metal panel to a plastic (“organic polymeric”) panel. While these may be joined with a variety of fasteners, or by welding or soldering, it is increasingly common to use an adhesive instead. The automobile and aerospace industries use high strength adhesives to form strong, long lasting bonds between substrates. Adhesives avoid the potential heat treatment of metals that can occur during welding, and also avoid any puncturing, and thus weakening, of the substrates that may be required when fasteners are used. Adhesive application can be readily controlled in automated manufacturing processes. Adhesives can be used to join a variety of components together. The use of adhesives also allows two component parts to be separated and a replacement for one component to be joined to the other with another application of an adhesive.
The strength of an adhesive bond between adhered substrates depends upon a variety of factors, including the strength of the bond between the adhesive and each substrate. This adhesive-substrate bond strength in turn depends upon several factors that include the condition and configuration of the substrate's surface when the adhesive is applied. Generally, at least some surface preparation treatments are carried out to prepare surfaces for receiving an adhesive. These might include cleaning off loose debris and degreasing. Of course, the larger the surface area that is bonded, the stronger the bond. Surface enlargement may be achieved by forming grooves or other irregularities on the surface. But, in some instances, such modifications may mechanically weaken or alter the substrate. Accordingly, such surface enhancement may not always be feasible or desirable.
Further, the longevity of an adhesive bond also depends on a variety of factors to which include the conditions it may be exposed to in ordinary use. For example, in the case of two metal panels adhered together, if one panel is subjected to higher temperatures than the other, it might be expected to expand thermally relative to the adhesive because plastic adhesives have low coefficients of thermal expansion relative to metals. Further, since adhesives are not good conductors of heat, the adhesive will conduct little heat to the other panel. This thermal expansion of one panel relative to the adhesive and to the other panel imposes heat-induced stresses on the adhesive bond. If the temperature of the one panel tends to cycle, the repeated cyclical heat-induced stresses may cause delamination.
Accordingly, it is desirable to provide adherends with enhanced surfaces for receiving an adhesive to produce stronger adhesive bonds. In addition, it is desirable to improve thermal conductivity between two substrates that are bonded together so that differential thermal expansion effects and the resultant tendency to delaminate are reduced Furthermore, other desirable features and characteristics of the enhanced adherend surfaces will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.